In order to minimize the complexity and cost of the air conditioning system, a plurality of flaps in the device for ventilation control is often controlled jointly by means of the same “mode disk”, i.e. a mechanical cam, and the actuator connected by means of the same to the cam. The drive is typically an electric motor or a rotary knob that can be set by hand.
In addition to temperature blending, another known practice is that of controlling the actual control flaps in the ventilation control device with a single cam and a single actuator. The air control flaps are assigned to corresponding air ducts and guide the respective air flows which are to be discharged via corresponding nozzles in the floor area (floor), at the front of the dashboard (panel) and under the windshield (defrost), for example.
In a modern ventilation control device, however, there is generally a dedicated guide cam for each flap on the cam (“mode disk”), said guide cam typically being operatively connected to the respective flap by a train of levers or links in order to adjust the flap. The guide cams are generally configured in such a way that the setting modes provided for air distribution determine the desired defined combination of air distribution flows, and do so in a typical recurring sequence. One example of a typical recurring sequence is: (A) air distribution only to the floor area “Floor” (B) air distribution to the dashboard and floor area “Panel & Floor” (C) air distribution only to the dashboard “Panel” (D) air distribution to the windshield and dashboard “Defrost & Panel” ←→ air distribution only to the windshield “Defrost” (F) air distribution to the windshield and foot area “Defrost & Floor”.
To reduce costs, an actuator without absolute position (rotation angle) feedback, e.g. a stepper motor or a brushless DC motor with a pulse counter (referred to as “DC pulse count motors”), is often used for driving the cam. To enable control by means of such a motor, a defined reference position is required. This is necessary for determining the position of the cam during operation.
One known solution for this purpose is to provide a mechanical stop on the cam, said stop interacting with a counterstop in order to define a reference position of the cam. As a result of this stop, no transition between the desired positions is possible at the angular position in which it is operative since the cam is not freely rotatable. If, for example, the mechanical stop is provided between the “Defrost & Floor” and the “Floor” setting in the direction of rotation in a ventilation device of the type in question offering the abovementioned combinations of “Floor” ←→“Panel & Floor” ←→ “Panel” ←→ “Defrost & Panel” ←→ “Defrost” ←→ “Defrost & Floor”, no direct transition from “Floor” to “Defrost & Floor” and vice versa is possible. In other words, the cam must be moved through all the settings in between, i.e. from “Floor”, via “Panel & Floor”, “Panel”, “Defrost & Panel” and via “Defrost” to reach the position “Defrost & Floor”. This may annoy the user since it gives rise to unwanted and unexpected behavior by the ventilation control device. Moreover, wear is increased since a longer setting distance has to be traveled on average because unwanted intermediate setting modes have to be passed through in order to reach the desired setting mode.